IDOMENI, Greece (Reuters) - Dozens of migrants and refugees were wounded on Sunday when Macedonian police fired tear gas and rubber bullets at crowds on the Greek side of the border, aid workers said, an act Athens called "dangerous and deplorable".

More than 10,000 migrants and refugees have been stranded at the Greek border outpost of Idomeni since February after a cascade of border shutdowns across the Balkans closed off their route to central and western Europe.

An earlier attempt by a large group of migrants to cross the border fence had resulted in the confrontation, a Macedonian official said.

Greece said police on the Macedonian side of their joint frontier used teargas, rubber bullets and stun grenades to push back the migrants. Macedonian authorities would only confirm they had used tear gas.

A deputy field coordinator with medical charity Medicins Sans Frontieres (MSF) told Reuters that, of around 300 people treated, more than 30 had injuries caused by rubber bullets.

A news release issued by MSF quoted one doctor with the charity saying said three children had been taken in to its field clinic with head injuries caused by rubber bullets.

Police in Skopje said three officers were also hurt.

Over a million people fleeing conflict poured into Europe, mainly through Greece, in the past year. The European Union is implementing an accord under which all new arrivals to Greece will be sent back to Turkey if they do not meet asylum criteria.

A Macedonian official who asked to remain anonymous said that a large group of migrants left Idomeni camp on Sunday morning and surged towards the fence.

"They threw rocks at the Macedonian police. The police fired tear gas in response," the official said.

"The migrants were pushing against the fence but standing on the Greek side of the border. The fence is still there, they have not broken through."

Reuters witnesses said a small group of migrants attempted to talk to Macedonian border guards, asking for them to open the border. After given a negative response, they and other migrants started walking towards the fence.

Macedonian police fired tear gas, and some migrants hurled back some gas canisters and rocks, they said.

"INDISCRIMINATE FORCE"

In an unusually strong statement, George Kyritsis, a spokesman for migration coordinators in the Greek government, said the use of force was unacceptable.

"The indiscriminate use of chemicals, rubber bullets and stun grenades against vulnerable populations, and particularly without reasons for such force, is a dangerous and deplorable act," Kyritsis said.

More than 50,000 refugees and migrants are stranded in Greece as a result of the border shutdowns. By Sunday morning, there were more than 11,200 people at Idomeni.

"We urge the authorities of FYROM to comprehend the potential risks the use of violence against refugees and migrants entails," said Kyritsis, referring to the official name of the neighboring country, Former Yugoslav Republic of Macedonia.

Athens has long refused to accept its neighbor as just 'Macedonia'. Some Greeks fear accepting 'Macedonia' could provide a basis for territorial claims by that country on a northern Greek province of the same name.

A Macedonian police spokesman said the situation at the border was under control but still tense, he added.

Achilleas Tzemos, MSF deputy field coordinator, told Reuters more than 300 people had been treated at the makeshift camp.

In addition to more than 30 treated for rubber bullet injuries, over 30 had open wounds and 200 had respiratory problems from tear gas exposure. "Among those with breathing difficulties were quite a few women and children," he said.

Greek authorities have been trying to convince the people to move to reception camps, but migrants have been refusing to move.